Microwave components

ABSTRACT

A microwave component with an at least partially enclosed cavity, such as a microwave filter, a waveguide or a horn antenna, includes an outer support structure and an electric layer which is made of pulse-plated silver and which is arranged on the inside of the support structure and faces the cavity. The microwave component further includes a first inner protective layer of chemically precipitated gold, the protective layer being arranged on the electric layer and facing the cavity.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/SE00/02019 which has an Internationalfiling date of Oct. 18, 2000, which designated the United States ofAmerica, the entire contents of which are hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates to microwave components with an at leastpartially enclosed cavity which are suitable for mass production andwhich satisfy high quality requirements. Examples of such microwavecomponents are microwave filters, waveguides and horn antennas. Theinvention further relates to a method of manufacturing such components.

BACKGROUND

The manufacture of products of the above-mentioned kind has up to nowbeen very complicated and expensive. Today the manufacture is primarilyperformed by working aluminium, inter alia by high-speed milling andsubsequent surface finishing, such as silver-plating, coating, etc. As aresult, it is time-consuming to manufacture each component and a greatnumber of manual operations are necessary. Furthermore, it is difficultto obtain the desired dimensional tolerances and quality of the productby this manufacturing process. Thus, as a rule these products needconsiderable after-treatment.

To solve these problems, the filter casings have, for instance, beenprovided with trimming means, which allow trimming of the filters afterfinal assembly. However, this makes the filters even more complicatedand expensive to manufacture. Moreover, this makes it necessary to testand trim each filter separately by a specialist.

The manufacturing process also significantly limits the possibility ofmanufacturing certain component parts. High-speed milling allows millingof simple geometric designs only, which makes it necessary tomanufacture complicated geometric designs in several pieces, which aresubsequently assembled into one functional unit. However, such assemblyof several subcomponents into a microwave component almost inevitablyleads to a lower degree of dimensional accuracy in the final product,which results in an even greater need for trimming, for instance, offilters after assembly. To arrange trimming means on the filters istime-consuming and considerably increases the costs.

The use of trimming means, such as trimming screws, and the assembly ofproducts from several including parts also constitute a risk of electricdisorders, so called passive intermodulation (PIM). In someapplications, this can be disastrous.

The making of the structural or supporting parts of aluminium alsolimits the thermal dimensional stability and the weight.

As an alternative, it has been proposed in JP 61 079 303 to manufacturewaveguides on fusible cores. Around this core, silver and copper areplated, and a carbon fibre fabric is subsequently wound around the coreuntil a thickness of about 2 mm. During the winding, the fabric isimpregnated with epoxy resin, and the wound support structure issubsequently cured by supplying heat and pressure, after which the coreis melted out. The resulting waveguide consists of a composite structurehaving continuous carbon fibres with an inner layer of copper andsilver.

However, also this manufacturing method suffers from a number ofdrawbacks. The method is expensive and complicated and requires a greatnumber of manual operations. Thus the method is not suitable for massproduction, and the manufacturing time for each component is long andthe costs are high.

In addition, the technique is not applicable to the manufacture offilter casings, since it is not possible to wind the carbon fibre fabricin the narrow, downwardly projecting, often circular cavities in thefilter casings, or corrugations in horn antennas.

Furthermore, in the prior-art wound carbon fibre waveguide the copperlayer cannot affect the rigidity and the thermal stability of thecomponent. In this case, the higher e-module of the carbon fibrestructure completely dominates the copper layer, and at temperaturechanges, which frequently occur in microwave components, this may causemicro-cracking problems in the metal layer. Other problems that mayarise are reduced adherence of the composite to the metal and galvaniccorrosion due to humidity entering the waveguide through the cracks. Thepresence of micro-cracks in microwave components, and especiallymicrowave filters, immediately results in reduced electric properties.

It is also a problem with prior-art microwave components that thesensitive electric layer, which internally faces the cavity, often getsdamaged either during the manufacturing process or during the use of thecomponent due to different types of environmental influence. This isvery serious, since it considerably changes and deteriorates thequalities of the component and usually makes it necessary to replace anddiscard the component.

Consequently, there is a need for microwave components which can bemanufactured at a lower cost and in a more efficient manner, inparticular on a large scale, and which also provide better products,have a greater resistance against environmental influence, improveddimensional accuracy, improved thermal dimensional stability, fewerincluding parts to be integrated and improved electric properties.

OBJECT OF THE INVENTION

Thus, the object of the present invention is to provide microwavecomponents with cavities, which wholly or at least partly obviate theabove-mentioned problems. The invention also provides a method ofmanufacturing such microwave components.

This object is achieved by means of a microwave component and a methodaccording to the appended claims.

SUMMARY OF THE INVENTION

The invention relates to microwave components with an at least partiallyenclosed cavity, comprising an outer support structure and an electriclayer, which is preferably made of silver and which is arranged on theinside of the support structure. The microwave components according tothe invention are distinguished in that they further comprise a firstinner protective layer of gold (D), said protective layer being arrangedon the electric layer (C) and facing the cavity.

The protective layer is preferably a chemically precipitated gold layer.By arranging such a protective layer, the sensitive electric layer isprotected against environmental influence and damage, at the same timeas the electric function is not affected to any substantial degree.Unlike prior-art methods of protecting silver surfaces for electric usein microwave components, a gold layer arranged directly on the silversurface has the advantage that it can be made thin, yet completelytight, and it also provides a lasting protection against theenvironment. In contrast to galvanically applied gold, a chemicallyapplied gold layer provides completely tight layers in the smallthicknesses that are electrically acceptable in these connections.

The structure of the electric layer is of great importance. Silveroffers by far the best electric properties compared with otherconducting materials. The electric properties have a great influence onthe performance of microwave components, The application of silver bypulse-plating additionally improves the evenness and tightness of thelayer. Pulse-plated silver also permits satisfactory macro spreading,thus allowing plating in narrow spaces, which is not possible byconventional direct-current plating. This is crucial as the cavitiesalmost exclusively have partial surfaces and edges that are located atdifferent distances from the power source. The addition of a protectingchemically precipitated gold layer on the silver layer has surprisinglybeen found to offer many advantages. A chemically precipitated goldlayer is considerably tighter than, for instance, galvanicallyprecipitated gold layers. One advantage of chemically precipitated goldon pulse-plated silver is thus that the even and tight silver isprotected by a gold layer which is very thin but still tight. Thealternative of using a galvanically applied gold layer requires aconsiderably thicker layer to attain the same tightness, usually morethan ten times thicker. Microwaves in a component penetrate into themetal layers and a great disadvantage of galvanically applied layers isthat the thicker gold layer reduces the electric properties of thecomponent due to the lower conductivity of the gold. In addition, theinferior electric properties are further deteriorated since thecomposition of the layer will be uneven as a consequence of the unevendistribution of the field strength. From the point of view ofproduction, galvanically applied layers are also disadvantageous,compared with chemically precipitated gold, due to longer manufacturingtime, increased thickness margin owing to unevenly composed layers,higher material costs as well as higher weight.

An alternative way of applying a gold layer is to passivate silver, forinstance, with an organic substance. But this is disadvantageous forseveral reasons. Unlike the precious metal gold, organic substancesreact with a number of substances which can change the composition ofthe surface. Organic substances allow diffusion of substances throughthe layer to a considerably larger extent and thus cannot afford such acomplete protection. The organic layer is less resistant to high fieldstrength. The organic layer has less temperature resistance and lessresistance to decomposition. When using organic layers, it is moreimportant that the layers be thin as organic layers are not electricallyconducting and thus have a detrimental effect on the electricproperties, such as conductivity. An organically composed layer does notprovide the same mechanical strength as a metal gold layer. As aconsequence, there is a considerably increased risk of the layerbreaking through in contact surfaces and other surfaces exposed to wear.If this happens, the electric signals can be influenced in anuncontrollable manner by the occurrence of differences in conductivityand insulation in the component.

On the other hand, it has surprisingly been found that the arrangementof a protective layer of chemically precipitated gold provides excellentprotection against environmental influence on the electric layer, at thesame time as the layer can be made so thin that the electric propertiesof the component will not be affected to any appreciable extent.

Furthermore, the outer support structure is preferably made of a castmaterial, such as a castable metal or a ceramic or plastic material, andmade in one integral piece. By using a castable material for themanufacture, the dimensional accuracy increases essentially, at the sametime as the manufacturing can be performed in a rapid and efficientmanner and is thus well suited for mass production of such components.Unlike, for instance, wound carbon fibre fabric, an integral supportstructure has omnidirectional mechanical and thermal properties. This isa great advantage, especially in case of complicated geometric designs,such as cavities in filter casings and corrugations in horn antennas. Inaddition, it is usually these geometric designs that have the narrowesttolerances of the components. The provision of a support structure withomnidirectional properties therefore contributes to a great extent toachieving satisfactory repeatability in mass production.

The outer support structure can, as an alternative, be composed of oneor more metal layers against the conducting silver layer.

Thanks to the improved properties of the microwave component accordingto the invention relative to parts which are formed by after-treatment,such as high-speed milling, and which are manufactured by winding or thelike, the finished component can be provided without trimming. Thismeans that it is possible to guarantee such a quality that extratrimming means, which were formerly necessary in many connections, canbe omitted which results in considerable savings. Furthermore, thePIM-levels will be very low and in most cases substantially negligible.Depending on the choice of material, improved dimensional stabilityunder heat, a lower weight of the product, improved environmentalresistance and extremely good dimensional accuracy are also obtained.

Thanks to the use of the cast or plated outer support structure, it isalso possible to provide geometrically complicated microwave components,such as integrated filter casings, waveguide systems and similarput-together products made in one piece, which facilitates assembly andreduces the risk of electric loss.

The composition structure according to the invention is in particularsuitable for microwave components with cavities for telecommunication,comprising a partially enclosed cavity and electric connections arrangedon at least one side of said cavity. The tolerance requirements for thistype of component are very critical, and therefore there is a great needof an improved product which reduces the need of after-treatment andtrimming. Due to the fact that the outer support structure is made inone integral piece, it is also possible to manufacture the entiremicrowave component, including the inner walls and the like and electricconnections for the coupling to the rest of the waveguide system, in onepiece. Consequently, it is possible to obtain high functionality withina small volume.

For essentially the same reasons, the inventive structure is furthersuitable for waveguides for microwaves, which waveguides comprise acavity and electric connections arranged on at least one side of saidcavity. The invention is particularly suitable for waveguides in whichthe cavity is bent in at least one plane and preferably in a pluralityof planes. Such complicated geometric designs are substantiallyimpossible to produce in one piece by present-day techniques. It is alsopossible to provide waveguides in which the cavity is twisted by meansof the inventive structure.

The outer support structure of the microwave components according to theinvention preferably has such dimensional tolerance and thermalstability at the inner surface that the electric requirements can befulfilled without trimming. Thus the need of after-adjustment andtrimming during assembly is avoided as well as the need of arrangingtrimming means on the component.

It is also possible to choose a material for the outer support structurethat is at least partially flexible and which allows at least somedegree of twisting or bending of the component. As a result, some degreeof flexibility can be imparted to the cavities of microwave components,and one type of component can be used in a great number of applications.This increases the usability of each product and improves thepossibilities of mass production in greater series.

Furthermore, for many purposes the outer support structure preferablycomprises zinc, tin or alloys of these materials, since all thesematerials are castable and have very good properties as regards thermalstability.

On the other hand, for other purposes the outer support structurepreferably comprises epoxy plastic material, which is further preferablyfilled with reinforcing particles of harder material, such asmicro-carboys or homogeneous micro-spheres, which particles preferablyhave a size in the range of 10-350 μm. The particles, which can also beused as filling in castable metals, increase the rigidity and thethermal stability of the material.

As concerns the dimensions, the outer support structure preferably has athickness that is less than 5 mm and the electric layer a thickness thatis less than 10 μm.

The inventive microwave component preferably comprises an inner supportstructure made, for instance, of copper, said support structure beingarranged between the outer support structure and the electric layer andadapted to impart improved thermal stability and/or mechanical strengthto the component in interaction with the outer support structure. Theuse of two support structures, one outer that is cast or plated in oneor more layers, and one inner that is for instance plated, provides anoften necessary possibility of trimming the mechanical and thermalproperties of the components by the choice of material combinations andlayer thicknesses of the structures. The thus-obtained interactionbetween the outer and the inner support structure is particularlyimportant when manufacturing microwave components with cavities in onepiece, which components lack after-trimming means. The tolerancerequirements as to the dimensions in this application are usuallyextremely narrow and often less than 10 μm. The inner support structureadvantageously has a thickness of between 5 and 200 μm. The innersupport structure, which preferably consists of copper, affects therigidity and thermal stability of the component and increases theadhesion of the inner surface. Unlike prior-art solutions, none of thesupport structures will in this case totally dominate the other, whichguarantees an efficient interaction between them. The support structurecan be composed of one or more layers.

It is also suitable for the protective layer to be arranged on theelectric layer, preferably so as to cover the same completely, and tohave such a small thickness, preferably less than 0.5 μm, that theelectric properties of the component are not affected to anyconsiderable extent.

In many cases, a protective layer, for instance of chemicallyprecipitated gold, is preferably arranged on the outer layer. It mayalso be advantageous to arrange a protective layer between the inner andthe outer support structure when the outer support structure is not madeof metal. In this way, the inner layers are protected against outsideenvironmental influence.

The invention also relates to a corresponding method of manufacturingthe microwave components according to that stated above.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail for the purpose ofexemplification by means of embodiments and with reference to theaccompanying drawings, in which

FIG. 1a is a schematic cross-sectional view of a part of a filter casingaccording to an embodiment of the invention;

FIG. 1b is a cross-sectional view on a larger scale of a part of thewall in the filter casing in FIG. 1a;

FIG. 2a is a lateral view of a waveguide according to an embodiment ofthe invention;

FIG. 2b is a top plan view of the waveguide in FIG. 2a; and

FIG. 3 is a schematic cross-sectional view of a corrugated horn antennaaccording to an embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The invention concerns microwave components with a new, improvedstructure, and a microwave filter, a waveguide and a horn antennaaccording to the invention will now be described in more detail.

FIG. 1a schematically shows a microwave filter for base stations formobile telephony according to the invention, comprising a microwavecomponent with a cavity, in this case a filter casing 10, and electricconnections, in this case connecting flanges (not shown), arranged on atleast one side of said cavity. The microwave filter has a wallconstruction which is schematically shown in FIG. 1b. The wall compriseson the outside an outer support structure A made of a cast material,such as a castable metal or a ceramic or plastic material. It is,however, also possible to use copper or other materials which are notcast as the outer support structure. The material should be chosen sothat the outer support structure has such dimensional tolerance andthermal stability that electric requirements can be met withouttrimming. Preferably, use is made of epoxy plastic material, which isfurther preferably filled with reinforcing particles of harder material,such as micro-carboys or homogeneous micro-spheres, to increase thethermal stability and the strength. These particles should have anominal particle size in the range of 10-350 μm. Plastic materials haveseveral advantages, such as being cheap and easy to treat. It is alsopossible to use zinc, tin or alloys of these materials. The outersupport structure suitably has a relatively great thickness to impartstrength to the component, but preferably less than 5 mm. Furthermore,the outer structure of the component should be made in one integralpiece.

On the inside of the outer support structure, an inner support structureB is preferably arranged, which is preferably made of metal, forinstance copper. This layer should be adapted to impart improved thermalstability and/or mechanical strength to the component in interactionwith the outer support structure. A suitable thickness of this layer isbetween 5 and 200 μm. It is in particular important to use an innersupport structure in the cases where plastic or ceramic materials areused for the outer structure, since the inner layer thus forms a barrierwhich protects the interiorly situated sensitive electric layer againstmoisture and the like which is being transferred in the outer layer,against thermal stress between the materials, etc.

Between the outer and the inner support structure, a protective layer,for instance made of chemically precipitated gold (not shown), canadvantageously be arranged to protect the inner layers against outsideenvironmental influence.

Subsequently, on the inner support layer the electric layer C isarranged, which is for instance made of silver. Gold or copper can,however, be used instead in some cases. When the inner support layer isomitted, the electric layer is arranged directly on the inside of theouter structure. The electric layer preferably has a thickness that issmaller than 10 μm.

On the inside of the electric layer, it is advantageous to arrange aprotective layer D, a so-called environment protecting means. This layerpreferably completely covers the electric layer and should have such asmall thickness that the electric properties of the component are notaffected to any considerable extent. Use is preferably made of athickness smaller than 0.5 μm. The protective layer can advantageouslybe a chemically precipitated gold layer. The protective layer isparticularly important when silver is used as electric layer material,since it protects the silver against sulfidation. In this case, it isalso particularly suitable to use chemically precipitated gold as aprotective layer.

FIG. 2 shows an inventive waveguide for microwaves, comprising a cavity,in this embodiment in the form of a waveguide part 20, and electricconnections, in this embodiment in the form of connecting flanges 21,22, arranged on both sides of said cavity 20. The waveguide has a wallstructure corresponding to that of the filter casing described above.This structure is particularly suitable for waveguides in which thecavity is bent in at least one plane and preferably in a plurality ofplanes, and the illustrated cavity is bent, on the one hand, in ahorizontal plane (see FIG. 2a) and, on the other, in a vertical plane(see FIG. 2b). Such integrally formed waveguides could not bemanufactured using prior-art structures and were therefore composed byjoining a plurality of different parts. Also with this structure thecavity can be twisted.

In particular in the case of waveguides, the outer support structureoften preferably comprises an at least partially flexible material. Thisallows at least some degree of twisting or bending of the component, andone and the came component can thus easily be adjusted to variousapplication situations. Such flexibility can, however, also be desirablein connection with other types of microwave components.

FIG. 3 schematically shows an inventive corrugated horn antenna formicrowaves. This horn antenna comprises an internally corrugated antennapart 30 and electric connections, here in the form of connecting flanges31, arranged on at least one side of said antenna part 30. The antennahas a wall structure corresponding to the wall structure of theabove-described filter.

When manufacturing the above-described type of microwave components, aninner core is first manufactured of a fusible material. This inner coreis given a shape corresponding to the desired cavity of the microwavecomponent which is to be manufactured. Especially narrow gaps, slits andthe like can be made in the core to form thin walls within themanufactured body. This is particularly desirable when manufacturing theinner walls of the microwave component surrounding the cavity, but alsowhen manufacturing the corrugation of horn antennas and the like. Theform tool, i.e. the inner core, is also preferably made by casting in amould, which makes the process easily repeatable as this mould can bereused.

Subsequently, round the inner core, an outer casting mould is arranged,which is filled with cast compound round the inner core. The choice ofcast compound depends on what application the component is intended forand has been discussed above. After the cast compound has been cured,the outer casting mould is removed, after which the inner core is meltedout of the cast product. Before or after melting out the inner core, theelectric layer is arranged on the inner surface of the cast product, asthe other layers described above. These layers are preferably applied tothe fusible inner core starting from the inside. The layers can, forinstance, be applied by plating by means of an electric or preferablychemical method. The chemical method provides an even deposition of thematerial over the surface, whereas the electric method provides a layerwhich gets thicker in the corners and similar places where the electricfield is reinforced and thinner on hidden surfaces where the field isweakened.

By means of chemical or electric methods, it is, as already mentioned,also possible to apply, for instance, copper as a protective layerinstead of arranging a cast support layer.

By means of the above method, the above-described structure of microwavecomponents can be obtained in a simple and efficient manner, and themethod also allows mass production. By carefully forming the outersurface of the core, which surface is relatively easy to work, it ispossible to obtain very good dimensional accuracy of the final productand especially of the sensitive inner surfaces which are facing cavitiesenclosed in the component. It is further easy to provide narrow and thininternal structures, such as walls, in the microwave components. It isalso possible by means of this method to manufacture several products inthe same process by using several form tools, which makes themanufacturing process considerably more efficient.

By means of the inventive method, it is also possible to manufacturemicrowave components in which additional components are integrated inthe cavity walls. In the walls of the tool that is used to manufacturethe fusible core, other pre-manufactured parts and components can befitted, before the tool is filled with the melt. These parts can bebars, spirals, walls, etc. They can also be integrated circuits whichare mounted, for in-stance, on ceramic plates or other insulating bases.The parts are subsequently enclosed by the melt after the filling.However, the part or parts which are inserted into the wall of the steeltool and which fix the part during filling will not be enclosed by themelt. When removing the core, the parts project from the wall of thecore. In the subsequent application of the support structure by platingor casting, the projecting parts are fixed into the wall of the cavity.Thus the fixing primarily takes place on the inside, but cooling flangesetc can, of course, be arranged on the outside in the same manner.

Instead of inserting the pre-manufactured parts into the steel tool,cavities can also be made in the core where the parts are placedafterwards. The advantage of the first variant is, however, that theparts can be inserted in different directions independently of how thesteel tool is removed from the core.

The advantages of the components and the method according to theinvention are, among other things, that a thermal expansion, CTE(Coefficient of Thermal Expansion), is obtained, which is considerablylower than that of e.g. aluminium. Another advantage is that morecomplex products can be manufactured. This is advantageous in electricapplications, resulting in fewer contact surfaces, better environmentalresistance, more stable electric performance, etc. Furthermore, themanufacture is cheap and allows a high rate of production. The finalproduct will also be better than by means of conventional methods. Theproduct can, for instance, be made lighter and thinner without reducedstrength and the like. Furthermore, the material has satisfactorydimensional accuracy and dimensional stability. By using a core, a formtool, around which the product is formed, it is also possible, asalready mentioned, to provide very thin walls and similar details, whichis essentially impossible by conventional methods.

During plating, the thickness of the walls of the body primarily dependson for how long the plating is allowed to last, but also on parameterssuch as temperature, the composition of the bath and pH.

The invention has been described by means of embodiments. It will,however, be understood that many variants of the invention, besidesthose described above, such as the use other materials, other methods ofarranging the different layers of material, the manufacture of the othermicrowave components, etc, are possible. Such obvious variants must beconsidered to fall within the scope of the invention such as defined bythe appended claims.

What is claimed is:
 1. A microwave component with an at least partiallyenclosed cavity, comprising: an outer support structure; an electriclayer, made of pulse-plated silver and arranged on the inside of thesupport structure and facing the cavity; and a first inner protectivelayer of chemically precipitated gold, said protective layer beingarranged on the electric layer and facing the cavity, wherein the cavityincludes a plurality of put-together cavities, the electric layers ofthe respective cavities being interconnected.
 2. A microwave componentas claimed in claim 1, wherein the protective layer covers substantiallycompletely the electric layer which faces the cavity.
 3. A microwavecomponent as claimed in claim 1, wherein the outer support structure ismade in one integral piece.
 4. A microwave component as claimed in claim1, further comprising electric connections which are connected to theelectric layer and arranged on at least one side of said cavity.
 5. Amicrowave component as claimed in claim 1, wherein the component is atleast one of a microwave filter and a multiplexer for telecommunication,comprising an at least partially enclosed cavity and electricconnections arranged on at least one side of said cavity.
 6. A microwavecomponent as claimed in claim 1, wherein the component is a waveguidefor microwaves, comprising a waveguide cavity and connecting flangesarranged on at least one side of said cavity.
 7. A microwave componentas claimed in claim 6, wherein the cavity is bent in at least one plane.8. A microwave component as claimed in claim 1, wherein the component isa corrugated horn antenna for microwaves, comprising an internallycorrugated antenna part and electric connections arranged on at leastone side of said antenna part.
 9. A microwave component as claimed inclaim 1, wherein the outer support structure has such thermal stabilityand the electric layer has such electric properties and dimensionaltolerances that electric requirements on the component can be fulfilledwithout trimming or similar adjustment after manufacture.
 10. Amicrowave component as claimed in claim 1, wherein the outer supportstructure comprises an at least partially flexible material which allowsat least some degree of twisting or bending of the component.
 11. Amicrowave component as claimed in claim 1, wherein the outer supportstructure is made of copper.
 12. A microwave component as claimed inclaim 1, wherein the outer support structure is made of a cast material,including at least one of castable metal and a ceramic or thermosettingplastic material.
 13. A microwave component as claimed in claim 12,wherein the outer support structure comprises at least one of zinc, tinand alloys of zinc or tin, which is further filled with reinforcingparticles of harder material, including at least one of micro-carboysand homogeneous micro-spheres, which particles have a size in the rangeof 10-350 μm.
 14. A microwave component as claimed in claim 12, whereinthe outer support structure comprises epoxy plastic material, which isfurther filled with reinforcing particles of harder material, includingat least one of micro-carboys and homogeneous micro-spheres, whichparticles have a size in the range of 10-350 μm.
 15. A microwavecomponent as claimed in claim 1, wherein the outer support structure hasa thickness less than 5 mm.
 16. A microwave component as claimed inclaim 1, wherein the electric layer has a thickness less than 10 μm. 17.A microwave component as claimed in claim 1, further comprising an innersupport structure made of copper, said support structure being arrangedbetween the outer support structure and the electric layer and adaptedto impart at least one of improved thermal stability and mechanicalstrength to the component in interaction with the outer supportstructure.
 18. A microwave component as claimed in claim 17, wherein theinner support structure has a thickness of between 5 and 100 μm.
 19. Amicrowave component as claimed in claim 17, further comprising a secondprotective layer arranged between the inner support structure and theouter support structure, which second protective layer includes achemically precipitated gold layer.
 20. A microwave component as claimedin claim 1, wherein the first protective layer has such a smallthickness that the electric properties of the component are not affectedto any considerable extent, and a thickness that is less than 0.5 μm.21. The microwave component of claim 1, wherein the cavity is bent in aplurality of planes.
 22. The microwave component of claim 7, wherein thecavity is bent in a plurality of planes.
 23. A microwave component asclaimed in claim 7, wherein the cavity is twisted.
 24. A microwavecomponent as claimed in claim 13, wherein the outer support structurecomprises epoxy plastic material, which is further filled withreinforcing particles of harder material, including at least one ofmicro-carboys and homogeneous micro-spheres, which particles have a sizein the range of 10-350 μm.
 25. A microwave component as claimed in claim18, further layer arranged between the inner support structure and theouter protective layer includes a chemically precipitated gold layer.26. A microwave component with an at least partially enclosed cavity,comprising: an outer support structure; an electric layer, made ofpulse-plated silver and arranged on the inside of the support structureand facing the cavity, and a first inner protective layer of chemicallyprecipitated gold, said protective layer being arranged on the electriclayer and facing the cavity, wherein the component is a waveguide formicrowaves, including a waveguide cavity and connecting flanges arrangedon at least one side of said cavity, and wherein the cavity is bent inat least one plane.
 27. A microwave component as claimed in claim 26,wherein the cavity comprises a plurality of put-together cavities, theelectric layers of the respective cavities being interconnected.
 28. Amicrowave component as claimed in claim 26, wherein the cavity istwisted.
 29. A microwave component as claimed in claim 26, wherein theprotective layer covers substantially completely the electric layerwhich faces the cavity.
 30. A microwave component as claimed in claim26, wherein the outer support structure is made in one integral piece.31. A microwave component as claimed in claim 26, further comprisingelectric connections which are connected to the electric layer andarranged on at least one side of said cavity.
 32. A microwave componentas claimed in claim 26, further comprising an inner support structuremade of copper, said support structure being arranged between the outersupport structure and the electric layer and adapted to impart at leastone of improved thermal stability and mechanical strength to thecomponent in interaction with the outer support structure.
 33. A methodof manufacturing microwave components with an at least partiallyenclosed cavity, comprising the steps of: manufacturing an inner coremade of a fusible material, which has a shape corresponding to that ofthe cavity of the microwave component which is to be manufactured;chemically precipitating a protective layer of gold on the core;arranging an electric layer of silver on the gold layer; arrangingoutside the electric layer an outer support structure; and melting outthe inner core.
 34. A method as claimed in claim 33, comprising theadditional step of inserting pre-manufactured parts, when manufacturingthe inner core, which are arranged so that they project from the core atleast with some part, and integrating these projecting parts in theouter support structure when arranging the same.
 35. A method as claimedin claim 34, wherein the projecting parts are also integrated with theelectric layer.
 36. A method as claimed in claim 33, wherein the step ofmanufacturing the inner core comprises the substeps of: arranging in acasting tool pre-manufactured parts, which are inserted with at leastsome part into the walls of the casting tool; inserting fusible materialinto the casting tool to cast the inner core; and separating the innercore together with the pre-manufactured parts arranged therein from thecasting tool.
 37. A method as claimed in claim 33, wherein the step ofmanufacturing the inner core comprises the substeps of: arranginginwardly protruding parts in a casting tool; inserting fusible materialinto the casting tool to cast the inner core; separating the inner corefrom the casting tool, cavities being formed in the positions of theinwardly protruding parts of the casting tool; and insertingpre-manufactured parts into the cavities so that they project from thecore with at least some part.
 38. The method as claimed in claim 35,wherein the projecting parts are integrated with the protective layer.